Wolf's Tech News: Advanced Format from Western Digital

Western Digital recently launch the first Advanced Format drives. It is develop as an education campaign about the technology. So what actually is the Advanced Format? It is actually the drives that uses 4KB sectors instead of the traditional 512 byte hard drive sector.

Hard drive uses Error Correcting Code (ECC) to find and correct any errors that occur. For a drive maker to add more space, they ultimately need to improve their error-correction capabilities, which means the necessary ECC data requires more space.

The problem is on ECC correction in 512B chunks, ECC can be more efficient when using a larger chunks of data. Even though larger sector rquires more ECC data than for a single 512B sector. But the overall ECC required on a larger sector is less than the sum of multiple sectors in order to maintain the same level of operational reliability. One estimate for 4K sector technology puts this at 100 bytes of ECC data needed for a 4K sector, while 320 (40x8) bytes for 8 X 512B sectors.

But this new format had a downside. There is a risk that a partition could be misaligned compared to the 4K physical sectors - where it would be unwittingly started in the middle of such a sector. As a result, the clusters of a file system on that partition would end up straddling 4K sectors, which would cause performance problems.